(W)Map finds that we are looking at the hot and cold spots in the microwave sky through a fog of electrons that have scattered about 20% of the photons from the early universe into and out of our line of sight. Our obscured vision means that the intrinsic features in the micrwoave sky are about 20% stronger than previously thought. This inference has important consequences for structure in the universe.
The inference comes from seeing a "reflection" of the features in the polarization. Just like glare from reflection of a surface, the scattered light is partially polarized. Because it is a reflection of the original pattern it is also correlated with the temperature variations. This correlation is what (W)MAP has detected. Because the scattering occurs in a thick screen relatively nearby this signal appears at large angles or low multipoles.
This thick screen of electrons is thought to come about through the (re)ionization of the universe by the first massive stars. The result implies that this process must have occured relatively early in the process of structure formation.
The implied increase in the intrinsic microwave temperature variations (before obscuration by reionization) also has implications for models of the origin of structure from quantum fluctuations in the early universe. It appears that the fluctuations on large scales seen by MAP are slightly larger than those seen at smaller scales by _other_ cosmological probes. This slight imbalance is known as tilt and if confirmed by future observations would have important implications for theories of the origin of structure.
